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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />For smaller basins (less than 30 S.M.), the rainfall events were investigated <br />using the Soil Conversation Services' (SCS) TR-20 model. The 500-year peak flow <br />due to rainfall was found to be much higher than the 500-year peak flow due to <br />snowmelt. The 50-, 100-, and 500-year regression lines were modified to <br />incorporate the discharge versus drainage area relationship obtained by the SCS <br />procedure. (The report descri bed above referenced di scharge-frequency data from <br />the 1975 Floodplain Study (Ref. 1) to be used in the current FIS.) <br /> <br />The Master Drainage Plan for Breckenridge (Ref. 3), prepared in 1986, contains <br />a statistical analysis of 21 individual gage stations. A regional frequency <br />analysis, similar to the analysis described for the 1978 study, was performed <br />to determine if the values from the 1978 study were still representative. The <br />results from the 1986 Master Plan Study as compared to the FEMA values were in <br />close agreement, therefore the FEMA values were considered still val id. Formulas <br />were derived for the 2-, 5-, 10-, 25-, 50-, and 100-year recurrence intervals. <br />The tributaries to the Blue River, which have drainage areas ranging from 0.8 to <br />11.1 square miles, were analyzed using the HEC-I computer model. The HEC-I run <br />provided runoff rates produced by rainfall. The results indicated that the peak <br />flow rates for the lower return periods such as 2-, 5-, 10-, and 25-year were <br />dominated by snowmelt values as calculated using the regional regression <br />analysis. For the 50- and 100-year floods, the HEC-I results were adopted as <br />peak flow rates. <br /> <br />6 <br />